Several people here have already mentioned Shakespeare, so it's perhaps worth noting, as anyone who's read a decent biography of him will know, that Shakespeare was the ultimate example of an author who wrote to make a living. He wasn't interesting in creating "great art" - his was the "mass entertainment" of its time; he had to fill a 3000 seat theatre six days a week in order to make a living. You can bet your life that if Shakespeare hadn't been able to make money from it, he wouldn't have done it. There's nothing wrong with the idea of writing to make money, even though some people in this thread have thrown scorn on the idea of anyone daring to want to do so.
Another example of a purely "commercial" writer is that (arguably) greatest of English novelists, Charles Dickens. Dickens was haunted throughout his life by the suffering he went through as a child as a result of his father being sent to a debtor's prison, and as a result, Dickens was utterly obsessed by money. He wrote to make money, and sued anyone who he felt was violating his rights. The "Harlan Ellison" of his day, one might say
. He was absolutely furious about the fact that American publishers made fortunes from his work, due to the lack of international copyright protection at the time, and many of his books (eg Nicholas Nickleby, David Copperfield) contain long diatribes about the poor copyright protection granted to authors.
I am the last person in the world to argue in favour of "perpetual copyright", but I am in favour of an author being able to get fair payment for his work.